Proposed studies will deal with the axenic growth in vitro of the larval stages of Schistosoma mansoni and S. japonicum, beginning with the miracidium. Growth and behaviour in vitro of the two species will be compared, and extent of development assessed at intervals by body measurements, and Feulgen stains of whole organisms to determine degree of nuclear multiplication. Labelled components will be incorporated in media to measure uptake and incorporation of various substances. The effect of different gas phases, presence or absence of antibiotics, different proteins, and other parameters on growth and development will be determined.